Process for the thermal decomposition of hydrocarbons



Dec. 11, 1934. F. M. PYZEL 1,983,992

PROCESS FUR THE THERMAL DECOMPOSITION 0F HYDROCARBONS Filed Aug. 18,1951 Patented Dec. 11, 1934 UNITED sTA Es PROCESS FOR THE THERMALDECOMPOSI- TION OF HYDROCARBONS Frederic Marinas Pysel, Piedmont, toShell Development Company,

Calif., assignor San Francisco,

Calif., a corporation of Delaware Application August 18, 1931, SerialNo. 557,880 7 Claims. (01. 22-212) This invention refers moreparticularly to the control of the thermal decomposition of hydrocarbon.into various products.

It has been found that in the'art of cracking hydrocarbon materialsdifferent types of compounds are produced at various temperatures. Inactual cracking'practice, most of these groups of products have beenmade simultaneously due mainly .to the fact that neither heating norreaction times can be controlled in an eflicient manner. Anotherdisadvantage of existing processes, particularly in cases when productsare to be made which require high temperatures, is that the heatcontained in the cracked product is often going to waste. V

I have found that such waste can be avoided and the production ofspecific groups of'cracked products can be accurately regulatedbyfirstly bringing a certain quantity of material to be cracked to atemperature at which those desired products are manufactured whichrequire the highest temperatures.

Into the hot cracked gases so produced I then inject in one or moresteps the same or different hydrocarbon materials to be cracked in sucha way and in such quantities that the temperatures to which a newmaterial is subjected and the time during which these new materials aresubjected to these conditions can be closely regulated.

A purpose of this invention is therefore to ac curately regulate thecracking of hydrocarbon material into various products.

Another purpose of this invention is to utilize the heat contained in astream of cracked material to crack additional quantities of hydrocarbonmaterial.

Further advantagesand features of my invention will be better and morefully understood from the following detailed description of a specificmanner of executing my invention, throughout which reference is made tothe attached drawing:

With reference to this drawing, 1) represents a vertical converterfilled with refractory material which is heated by means of burners (2).Hydrocarbon fuel is delivered to these burners through suitable piping-(3). A control valve (4) is placed in this line to control the flow offuel to the burners. Individual burners may be regu-' lated by smallervalves (5). Air controlled by a valve (25) is supplied to the converterthrough a manifold (6) connected to a blower (7). The air is forced intothe converter adjacent the burners (2). A stack (8) is connected to thelower part of the converter. The top of .the stack has a valve (9)opening into the atmosphere. A'steam line (10) controlled by valve (11)is connected with the stack near the top. Another line (12) foradmitting hydrocarbons, is controlled by a valve (13) and is connectedto the stack close to its top. At the top .of the converter, a valve(14) which can be opened to the atmosphere may be used A hydrocarbonline 15) controlled by a valve (16) discharges into the oiftake pipefrom the top of the converter. This pipe (1'1) leads from the top of theconverter and is connected to a downcomer pipe (18) which has a closedend (19). Other hydrocarbon injectors such as (23) and (24) may beplaced in the ofltake pipe and downcomer. Apipe Joining the downcomerleadsinto a wash box (20) having an upper outlet (21) and a lower outletvalve (22) An overflow pipe is-connected to the side of the wash box.

The operationof the system is as follows: Valves (4) and (9) being openand with valve (14) shut, hydrocarbon is admitted to burners (2). Thenecessary air for combustion is supplied through manifold (6) fromblower ('1).

The flames are directed downward and heat the refractory material in thebody of the converter. When the temperature of the refractory materialhas been raised to the desired point, heating is stopped by closingvalve (4) and shutting off the air blast. The stack valve (9) is closedand hydrocarbon material to be decomposed is admitted to the apparatusthrough pipe (12). This hydrocarbon is somewhat heated by the hot stackand is decomposed by coming into contact with the hot refractorymaterial in the converter. ,The cracked products are carried up throughthe converter and are discharged into pipe (1'1). Hydrocarbon materialmay be added through pipes (15), (23) and (24). Through which of theseinjectors hydrocarbon'is added will depend upon operating conditions. Asthe stream is carried along pipe (17) and through the downcomer pipe(18) the newly added material becomes mixed with the gases that issuedfrom the converter and is therebythermally decomposed. From the bottomof the downcomer the stream is led into the wash box (20) where thecarbon is separated from the gaseous and more volatile constituents. Thecarbon is removed from the wash box through pipe (25) to suitablefilters or centrifuges. The other products are removed by pipe (21) forsubsequent treatment.

After hydrocarbon material to be cracked has been passed into theconverter for some time, the refractory material becomes too cool forefficient conversion. It is therefore necessary to stop the flow ofhydrocarbon material and reheat. However, if the burners (2) were atonce started, hydrocarbon mixtures present in the converter might causean explosion, It is therefore advisable to first remove any combustiblematerial remaining in the converter. For this purpose steam line (10) isprovided. Hydro carbon entering through lines (12) and (15) is first.shut off. The valve (14) in the top of the converter may then be opened.steam from line (10) is forced through the refractory material tothoroughly purge it of any combustible material before commencing toreheat. Having completely purged the converter, the steam is shut off,valve (14) is closed, stack valve (9) is opened and the burners lighted.The control of the reaction time and the temperature at which reactiontakes place can be closely regulated by my process. With a given rate offlow of gases from the converter, the time of cracking can be controlledby the distance of the injection point from the wash box. Thetemperature at which the hydrocarbon material is cracked can becontrolled by the relative proportions of hydrocarbon added insuccessive steps. This temperature can also be controlled by thetemperature at which the hydrocarbon is introduced into the stream andalso by the physical state in which it is introduced. I

As an example of the use to which my invention can be put, I may cracknatural gas to produce a gas rich in hydrogen to be used for thesynthetic production of ammonia.

The gas used as raw material in this example for both the first stageconversion and for the subsequent second stage conversion was a naturalgas. containing principally methane and ethane in the proportions ofeighty-three parts methane to seventeen parts ethane.

The natural gas is cracked in the converter by being passed through thechecker work which has been heated ,to the desired temperatures; forinstance, about 2000 F. The gas issuing from the converter will becomposed principally of hydrogen and methane.

A typical analysis of this gas being:-

content as well as producing small amounts of ethylene, ethane, benzoland other hydrocarbons in the gas stream.

The following is an analysis of the final gas stream I have obtained:-

Per cent by volume CO: 0.4 Cal-I: I 0.15 .'C:H4' 1.03 Other cnfim 0.32O: 0.2 CO 10.0 ,H: 67.4 084 18.1 N: 2.8

A particular benefit of my method of operation is that a gas can beproduced with a controlled ethylene content. When natural gas is crackedfor the production of hydrogen small amounts of acetylene are foFned. Inthe past the acetylene in the gas stream has caused considerable troubleto operators owing to the explosive nature of this hydrocarbon, whensubmimd to pressure....'1his danger becomes particularly pronounced whenfurther separation of the gases is made in a low temperaturecondensation and fractionation apparatus. It has been found thatethylene which liquefies at a temperature comparatively near thetemperature at which acetylene solidifies has the power of dissolvingany acetylene which ac cumulates in the low temperature condensationapparatus if said ethylene is present in the apparatus in sufficientamounts. By controlling the ethylene content I can influence theproportion of these two hydrocarbons in such a way that theprecipitation of solid acetylene in the fraction vantageous to injectspecial hydrocarbons or hydrocarbon mixtures containing less methane andmore heavier hydrocarbons, the cracking conditions being. adjusted so asto obtain the desired products. I I 1 Besides the specific example of'an application of my invention as shown above, I mayadapt my inventionto various cracking requlrenients; I may for this purpose dispense withthe refractory filled converter and make use of other types of crackingapparatus. I may also apply pressure to the apparatus. I

In using my invention with different types of cracking apparatus theprinciple on which the invention is based is followed, namely, to firstapply the highest temperature to obtain the products which require thehighest conversion temperature and thereafter inject further quantitiesof hydrocarbon to obtain products which require a lesser temperature toeffect formation.

I claim as my invention:

1. In a process of producing hydrogen the steps comprising: passinghydrocarbon gas over highly heated refractory material in a converter,injecting hydrocarbon into the hot gases issuing from the converter,thereby producing ethylene in the gas stream and subsequently removingacetylene from the gas stream by theuse of said ethylene.

2. In a process producing hydrogen, the steps comprising: thermallydecomposing a hytirocai' bon gas to produce a reformed gas containinghydrogen and acetylene, producing ethylene in said reformed gas byinjecting amounts of hydrocarbon into the reformed gas and subsequentlyremoving the acetylene of the reformed gas by the aid of said ethylene;I

3-. In a process of producing hydrogen, the steps comprising: thermallydecomposing hydrocarbon gas to produce a .reformed gas containinghydrogen and acetylene-producing ethylene in said reformed gas byinjecting amounts of hydrocarbon into the reformed gas stream and insubsequent fractionation dissolving the acetylene in the ethylene. I I

4. In a process of producing hydrogen, the steps comprising: thermallydecomposing-hydrocarbon gas to a reform gas containing hydrogen, aceylene and'ethylene, increasing the ethylene content of the reform gas byinJecting amounts of hydrocarbon into the reformgas stream and in subseqent'fractionation dissolving the acetylene in tbet y ena 5. In a processof producing a hydrogen containing gas the steps comprising: passinghydrocarbon material into a refractory filled converter, producing areformed gas containing acetylene and hydrogen in said converter,allowing said reformed gas to issue from the converter injectinghydrocarbon material into the reformed gas stream rising from theconverter, producing ethylene in the gas stream and thereafter in thefractionation of the reform gas, acetylene in the ethylene.

6. In a process of producing a hydrogen containing gas the stepscomprising: passing hydrocarbon material into a heated refractory filledconverter, producing a gas containing acetylene and hydrogen in saidconverter, withdrawing said gas from the converter, injectinghydrocarbon material into the stream of gases withdrawn, prodissolvingthe ducing ethylene in said stream of withdrawn gases by means ofthethermal decomposition of said injected hydrocarbon material and insubsequent fractionation of said gas stream dissolving the acetylene inthe ethylene.

'7. In a process of producing a hydrogen containing gas the stepscomprising: passing natural gas into a heated refractory filledconverter, producing a reformed gas containing acetylene and hydrogen insaid converter, withdrawing the reformed gas from the converter,injecting natural gas into the reformed gas stream, ethylene in saidreformed gas stream by the thermal decomposition of the injected naturalgas, thereafter in a liquefaction process of gas fractionationdissolving the acetylene in the ethylene.

FREDERIC MARINUS PYZEL.

producing

